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The Digestive System


Chapter 24 The Digestive System Lecture Outline * Principles of Human Anatomy and Physiology, 11e Principles of Human Anatomy and Physiology, 11e Principles of Human ... – PowerPoint PPT presentation

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Title: The Digestive System

Chapter 24
  • The Digestive System
  • Lecture Outline

  • The main purpose of the digestive system it to
    break food down into small particles that can be
    absorbed and turned into energy.
  • The medical professions that study the
    structures, functions, and disorders of the
    digestive tract are gastroenterology for the
    upper end of the system and proctology for the
    lower end.

  • The gastrointestinal tract is the tube open at
    both ends for the transit of food during
    processing. The functional segments of the GI
    tract include the mouth, esophagus, stomach,
    small intestine, and large intestine.
  • The accessory structures that contribute to the
    food processing include the teeth, tongue,
    salivary glands, liver, gallbladder, and pancreas.

  • Digestion includes six basic processes.
  • Ingestion is taking food into the mouth (eating).
  • Secretion is the release of water, acid, buffers,
    and enzymes into the lumen of the tract.
  • Mixing and propulsion result from the alternating
    contraction and relaxation of the smooth muscles
    within the walls of the GI tract.
  • Digestion
  • Mechanical digestion consists of movements of the
    GI tract that aid chemical digestion.
  • Chemical digestion is a series of catabolic
    reactions that break down polymers into monomers.
  • Absorption is the passage of end products of
    digestion from the GI tract into blood or lymph
    for distribution to cells.
  • Defecation is emptying of the rectum, eliminating
    indigestible substances from the GI tract.

  • There are 4 layers in the GI tract, from inside
    to outside they are
  • Mucosa
  • Submucosa
  • Muscularis
  • Serosa

  • Inner lining of the GI tract
  • Composed of 3 sub-layers
  • Epithelium protects the organs, forms tight
  • Lamina propria contains blood vessels, absorbs
  • Muscularis mucosae increases surface area,
    absorbs nutrients

  • Connective tissue that binds the mucosa to the
  • Contains blood vessels, neurons, and glands

  • Contains skeletal muscles
  • Moves food along the GI tract

  • Found only in the abdominopelvic cavity
  • Used mainly for secretion

Nervous System Control
  • Enteric Nervous System ENS
  • -100 million neurons from esophagus to anus
  • Contains motor, sensory, and interneurons
  • Sense chemical interactions and when there is
    food in the GI tract

Nervous System Control
  • Autonomic Nervous System
  • Sympathetic and parasympathetic nerves connect
    the GI tract to the spinal cord and the brain
  • Emotions such as fear, anger, and stress may slow
    down the GI tract, causing nausea, diarrhea,
    vomiting, or lack of appetite.

  • The peritoneum is the largest serous membrane of
    the body.
  • Surrounds all organs in the digestive system
  • There are 5 large folds in this membrane, which
    helps to bind organs to each other

Clinical Application
  • Peritonitis is an acute inflammation of the
  • Cause
  • contamination by infectious microbes during
    surgery or from rupture of abdominal organs

Organs of the Digestive System
  • 1. Mouth, pharynx, esophagus
  • 2. Gallbladder
  • 3. Pancreas
  • 4. Liver
  • 5. Stomach and appendix
  • 6. Small intestine
  • 7. Large intestine, rectum, anus

  • The mouth (oral cavity) is formed by the cheeks,
    hard and soft palate, lips, and tongue.
  • The vestibule is made up cheeks, lips, gums and
  • The oral cavity proper is the opening between the
    oral cavity and the pharynx.

Salivary Glands
  • Saliva is secreted by the salivary glands, which
    lie outside the mouth and pour their contents
    into ducts that empty into the mouth
  • Saliva lubricates and dissolves food and starts
    the chemical digestion of carbohydrates. It also
    functions to keep the mucous membranes of the
    mouth and throat moist.
  • Saliva is 99.5 water and 0.5 solutes such as
    salts, dissolved gases, various organic
    substances, and enzymes.

Structure and Function of the Tongue
  • The tongue, together with its associated muscle,
    forms the floor of the oral cavity. It is
    composed of skeletal muscle covered with mucous
  • Muscles permit the tongue to be moved to
    participate in food manipulation for chewing and
    swallowing and in speech.

Structure and Function of the Teeth
  • The teeth project into the mouth and are adapted
    for mechanical digestion.
  • A typical tooth consists of three principal
    portions crown, root, and neck.
  • Teeth are composed primarily of dentin, a
    calcified connective tissue.

  • There are two dentitions, or sets of teeth, in an
    individuals lifetime deciduous (primary), milk
    teeth, or baby teeth and permanent (secondary)
  • Primary or baby teeth
  • 20 teeth that start erupting at 6 months
  • 1 new pair of teeth per month
  • Permanent teeth
  • 32 teeth that erupt between 6 and 12 years of age
  • differing structures indicate function
  • incisors for biting
  • canines or cuspids for tearing
  • premolars molars for crushing and grinding food

Digestion in the Mouth
  • Mechanical digestion (mastication or chewing)
  • breaks into pieces
  • mixes with saliva so it forms a bolus
  • Chemical digestion
  • amylase
  • begins starch digestion at pH of 6.5 or 7.0 found
    in mouth
  • when bolus enzyme hit the pH 2.5 gastric juices
    hydrolysis ceases
  • lingual lipase
  • secreted by glands in tongue
  • begins breakdown of triglycerides into fatty
    acids and glycerol

  • The pharynx is a funnel-shaped tube that extends
    from the nose to the junction of the esophagus
    and the larynx.
  • It is composed of skeletal muscle and lined by
    mucous membrane.
  • A flap of skin called the epiglottis is at the
    bottom of the pharynx.
  • It closes the esophagus when you breath or talk,
    and closes the trachea when you eat or drink.

  • The esophagus is a collapsible, muscular tube
    that lies behind the trachea and connects the
    pharynx to the stomach.
  • The role of the esophagus is to secrete mucus and
    transport food to the stomach.

  • Deglutition is swallowing.
  • Its how a bolus moves from the mouth to the
    stomach. It is facilitated by saliva and mucus
    and involves the mouth, pharynx, and tongue.
  • Peristalsis, wave like muscle contractions, push
    the bolus down the esophagus.
  • Solids 4-8 seconds
  • Liquids 1 second

  • The stomach is a J-shaped enlargement of the GI
    tract that begins at the bottom of the esophagus
    and ends at the pyloric sphincter
  • It serves as a mixing and holding area for food,
    begins the digestion of proteins, and continues
    the digestion of triglycerides, converting a
    bolus to a liquid called chyme.
  • Almost NO absorption at all occurs in the stomach.

The Stomach
  • It serves as a mixing and holding area for food,
    begins the digestion of proteins, and continues
    the digestion of triglycerides, converting a
    bolus to a liquid called chyme.
  • Parts of stomach
  • fundus---top
  • Body--middle
  • pylorus---starts to narrow as approaches pyloric
  • Empties as small squirts of chyme leave the
    stomach through the pyloric valve

Chemical Digestion in the Stomach
  • Chemical Digestion
  • Chemical digestion consists mostly of the
    conversion of proteins into peptides by pepsin,
    an enzyme that is most effective in the very
    acidic environment (pH 2) of the stomach. The
    acid (HCl) is secreted by the stomachs parietal
  • Gastric lipase splits certain molecules in
    butterfat of milk into fatty acids and
    monoglycerides and has a limited role in the
    adult stomach.

Mechanical Digestion
  • Gentle mixing waves
  • every 15 to 25 seconds
  • mixes bolus with 2 quarts/day of gastric juice to
    turn it into chyme (a thin liquid)

Anatomy of the Pancreas
  • The pancreas is divided into a head, body, and
    tail and is connected to the small intestine and
    the liver.
  • 5" long by 1" thick

Pancreas - Overview
  • Pancreatic juice contains enzymes that digest
  • starch (pancreatic amylase)
  • proteins (trypsin, chymotrypsin, and
  • fats (pancreatic lipase)
  • nucleic acids (ribonuclease and
  • It also contains sodium bicarbonate which
    converts the acid stomach contents to a slightly
    alkaline pH (7.1-8.2)
  • Pancreatic cancer is nearly always fatal and in
    the fourth most common cause of cancer death in
    the United States.

  • The liver is the heaviest gland in the body
  • The liver is divisible into left and right lobes
  • The gallbladder is a sac located in a depression
    on the posterior surface of the liver

Anatomy of the Liver and Gallbladder
  • Liver
  • weighs 3 lbs.
  • below diaphragm
  • right lobe larger
  • gallbladder on right lobe
  • size causes right kidney to be lower than left
  • Gallbladder
  • fundus, body neck

Histology of the Liver
  • Bile is secreted by hepatocytes. It digests fats
    in the small intestine.
  • Bile passes into bile ducts to the pancreas,
    where it is stored until released to the small

Bile Production
  • One quart of bile/day is secreted by the liver
  • yellow-green in color pH 7.6 to 8.6
  • Components
  • water cholesterol
  • bile salts Na K salts of bile acids
  • bile pigments (bilirubin) from hemoglobin
  • globin a reuseable protein
  • heme broken down into iron and bilirubin

Other Liver Functions
  • Detoxifies the blood by removing or altering
    drugs hormones(thyroid estrogen)
  • Removes the waste product--bilirubin
  • Releases bile salts help digestion by
  • Stores fat soluble vitamins-----A, B12, D, E, K
  • Stores iron and copper
  • Phagocytizes worn out blood cells bacteria
  • Activates vitamin D (the skin can also do this
    with 1 hr of sunlight a week)

Small Intestine
  • The major events of digestion and absorption
    occur in the small intestine.
  • The small intestine extends from the stomach to
    the large intestine.

Anatomy of the Small Intestine
  • 20 feet long----1 inch in diameter
  • Large surface area for majority of absorption
  • 3 parts
  • duodenum---10 inches
  • jejunum---8 feet
  • ileum---12 feet

Surface Area of the Small Intestine
  • Villi
  • 1 Millimeter tall
  • Finger like projections on the walls of the
  • Increase surface area
  • Microvilli
  • cell surface feature known as brush border
  • Even smaller than the villi

Functions of Microvilli
  • Absorption and digestion
  • Digestive enzymes found at cell surface on
  • Digestion occurs at cell surfaces
  • Significant cell division within intestinal
    glands produces new cells that move up
  • Once out of the way---rupturing and releasing
    their digestive enzymes proteins

Mechanical Digestion in the Small Intestine
  • Segmentation, the major movement of the small
    intestine, is a localized contraction in areas
    containing food (much weaker than in the stomach)
  • Peristalsis propels the chyme onward through the
    intestinal tract.

Chemical Digestion in the Small Intestine
  • Carbohydrates are broken down to glucose by
  • Proteins are broken down to amino acids by
    proteases and peptidases
  • Nucleic acids are broken down to nucleotides by
  • Lipids are broken down to glycerol and fatty acid
    tails by lipases

Anatomy of Large Intestine
  • 5 feet long by 2½ inches in diameter
  • Extends from small intestine to anus
  • Goes from cecum to ascending colon to descending
    colon to rectum to anus
  • Rectum last 8 inches of GI tract anterior to
    the sacrum coccyx

Chemical Digestion in Large Intestine
  • No enzymes are secreted only mucous
  • Bacteria ferment
  • undigested carbohydrates into carbon dioxide
    methane gas
  • undigested proteins into simpler substances
  • Bacteria produce vitamin K and B in colon

Absorption and Feces Formation in the Large
  • The large intestine absorbs water, electrolytes,
    and some vitamins.
  • Feces consist of water, inorganic salts,
    sloughed-off epithelial cells, bacteria, products
    of bacterial decomposition, and undigested parts
    of food.
  • Although most water absorption occurs in the
    small intestine, the large intestine absorbs
    enough to make it an important organ in
    maintaining the bodys water balance.

Defecation Reflex
  • The elimination of feces from the rectum is
    called defecation.
  • Defecation is a reflex action aided by voluntary
    contractions of the diaphragm and abdominal
    muscles. The external anal sphincter can be
    voluntarily controlled (except in infants) to
    allow or postpone defecation.

Doctors Office Poster
  • Choose an organ (stomach, small intestine, large
    intestine, liver, pancreas, gall bladder)
  • Create an illustrated, informative poster like
    you would find hanging in a doctors office.
  • The poster should be high quality, fully
    illustrated and labeled, and include text
    explaining BOTH the anatomy and physiology of the
  • Due Monday 5/21!

Regulation of Gastric Secretion and Motility
  • Cephalic phase
  • Gastric phase
  • Intestinal phase

Cephalic phase
  • The smell, sight, thought, or taste of food
    activates the cerebral cortex, the hypothalamus,
    and the brain stem.
  • You begin to secrete saliva, and your stomach
    secretes gastric juices.

Gastric Phase Stomach Working
  • Your nervous and endocrine systems secrete nerve
    impulses and hormones
  • This triggers peristalsis and the release of
    digestive enzymes

Intestinal phase
  • The intestinal phase begins when food enters the
    small intestine.
  • The stomach slowly release chyme so the small
    intestine isnt overloaded.

Development of the Digestive System
  • During the 4th week of development, the mesoderm
    of the embryo forms the gastrointestinal cavity
  • Until the 8th week of pregnancy, the digestive
    system is in a sac outside the body of the embryo
  • By the 20th week of pregnancy, the digestive
    system is fully formed and the fetus can swallow
    amniotic fluid

Aging and the Digestive System
  • Changes that occur
  • decreased secretory mechanisms
  • decreased motility
  • loss of strength tone of muscular tissue
  • changes in neurosensory feedback
  • diminished response to pain internal stimuli
  • Symptoms
  • sores, loss of taste, peridontal disease,
    difficulty swallowing, hernia, gastritis, ulcers,
    malabsorption, jaundice, cirrhosis, pancreatitis,
    hemorrhoids and constipation
  • Cancer of the colon or rectum is common

Diseases and Disorder
  • Dental caries, or tooth decay, is started by
    acid-producing bacteria that reside in dental
    plaque, act on sugars, and demineralize tooth
    enamel and dentin with acid.
  • Periodontal diseases are characterized by
    inflammation and degeneration of the gingivae
    (gums), alveolar bone, periodontal ligament, and

  • Peptic ulcers are crater-like lesions that
    develop in the mucous membrane of the GI tract in
    areas exposed to gastric juice.
  • Can lead to bleeding, anemia
  • Caused by stress (excess acid), bacteria, and
    drugs like aspirin

  • Hepatitis is an inflammation of the liver and can
    be caused by viruses, drugs, and chemicals,
    including alcohol.
  • Hepatitis A (infectious hepatitis) is caused by
    hepatitis A virus and is spread by fecal
    contamination. It does not cause lasting liver
  • Hepatitis B is caused by hepatitis B virus and is
    spread primarily by sexual contact and
    contaminated syringes and transfusion equipment.
    It can produce cirrhosis and possibly cancer of
    the liver. Vaccines are available to prevent
    hepatitis B infection.

  • Hepatitis C is caused by the hepatitis C virus.
    It is clinically similar to hepatitis B and is
    often spread by blood transfusions. It can cause
    cirrhosis and possibly liver cancer.
  • Hepatitis D is caused by hepatitis D virus. It is
    transmitted like hepatitis B and, in fact, a
    person must be co-infected with hepatitis B
    before contracting hepatitis D. It results in
    severe liver damage and has a high fatality rate.
  • Hepatitis E is caused by hepatitis E virus and is
    spread like hepatitis A. It is responsible for a
    very high mortality rate in pregnant women.

  • Anorexia nervosa is a chronic disorder
    characterized by self-induced weight loss
  • Caused by body-image and other perceptual
    disturbances, or genetics.
  • Individuals may become emaciated and may
    ultimately die of starvation or one of its
    complications. Treatment consists of
    psychotherapy and dietary regulation.

Gastroesophageal Reflex Disease
  • Acid reflux, heartburn, GERD
  • stomach acids enter esophagus
  • for a weak sphincter---don't eat a large meal
    and lay down in front of TV
  • smoking and alcohol make the sphincter relax
    worsening the situation
  • Control the symptoms by avoiding
  • coffee, chocolate, tomatoes, fatty foods, onions
  • take Tagamet HB or Pepcid AC 60 minutes before
  • neutralize existing stomach acids with Tums

  • Inflammation of the appendix due to blockage of
    the lumen by chyme, foreign body, carcinoma,
    stenosis, or kinking
  • Symptoms
  • high fever, elevated WBC count, neutrophil count
    above 75
  • referred pain, anorexia, nausea and vomiting
  • pain localizes in right lower quadrant
  • Infection may progress to gangrene and
    perforation within 24 to 36 hours

Lactose Intolerance
  • Mucosal cells of small intestine fail to produce
  • essential for digestion of lactose sugar in milk
  • undigested lactose retains fluid in the feces
  • bacterial fermentation produces gases
  • Symptoms
  • diarrhea, gas, bloating abdominal cramps
  • Dietary supplements are helpful

  • Myxovirus that attacks the parotid gland
  • Symptoms
  • inflammation and enlargement of the parotid
  • fever, weakness sore throat (especially
    swallowing sour foods)
  • swelling on one or both sides
  • Sterility rarely possible in males with
    testicular involvement (only one side involved)
  • Vaccine available since 1967

  • Pancreatitis---inflammation of the pancreas
    occurring with the mumps
  • Acute pancreatitis---associated with heavy
    alcohol intake or biliary tract obstruction
  • result is patient secretes trypsin in the
    pancreas starts to digest itself

  • Vomiting is the forcible expulsion of the
    contents of the upper GI tract (stomach and
    sometimes duodenum) through the mouth.
  • Prolonged vomiting, especially in infants and
    elderly people, can be serious because the loss
    of gastric juice and fluids can lead to
    disturbances in fluid and acid-base balance
  • Cause
  • irritation or distension of stomach
  • unpleasant sights, general anesthesia, dizziness
    certain drugs

Defecation Problems
  • Diarrhea chyme passes too quickly through
  • H20 not reabsorbed
  • Constipation--decreased intestinal motility
  • too much water is reabsorbed
  • remedy fiber, exercise and water

  • In root canal therapy all traces of pulp tissue
    are removed from the pulp cavity and root canal
    of a badly diseased tooth
  • The branch of dentistry that is concerned with
    the prevention, diagnosis, and treatment of
    diseases that affect the pulp, root, periodontal
    ligament, and alveolar bone is known as
  • Orthodontics is a dental branch concerned with
    the prevention and correction of abnormally
    aligned teeth.
  • Periodontics is a dental branch concerned with
    the treatment of abnormal conditions of tissues
    immediately around the teeth.

  • Diverticula are saclike outpouchings of the wall
    of the colon in places where the muscularis has
    become weak.
  • The development of diverticula is called
  • Inflammation within the diverticula, known as
    diverticulitis, may cause pain, nausea, vomiting,
    and either constipation or an increased frequency
    of defecation. High fiber diets help relieve the
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